Intensive research efforts in developing microfluidic systems have been pursued by academic and industrial institutions over recent years. These microfluidic devices and apparatus are developed for performing various fluidics-related functions, processes and activities. Almost all microfluidic devices involve manipulating, handling, and processing molecules and particles. However, up to now, there is not a general method for manipulating molecules in microfluidic devices. Some examples of physical methods for manipulating molecules used in biochips include electric field based electrophoresis, optical radiation force related optical tweezers and others. All these methods have many limitations. Electrophoresis utilizes direct current (DC) electrical field. Generating sufficient DC field in aqueous solutions without causing undesired effects, e.g., surface electrochemistry, gas bubble generation, is very difficult. Electric field can only guide molecules either with or against with the field direction. There won't be any force induced if the molecule charges are small. Most importantly, the DC electrical field cannot be readily structured to generate manipulation forces in a versatile way. Also, electrode polarization determines that over 80% of the applied DC voltage is dropped across the electrode-solution double layer and there is only a very small percent of the applied voltage that is actually across the bulk solution. Optical radiation force can operate on large molecules, e.g., DNA molecules, but there are certain difficulties in generating 3-D, flexible, optical manipulation forces.
Despite the existence of a number of physical forces applicable to molecule manipulation, several key difficulties exist. First, many physical forces are proportional to the volume of the particles that are manipulated. Direct manipulation of many types of molecules with these forces requires extremely high field strength because of the relative small dimensions of molecules, and effective manipulation of molecules is almost impossible. High field strengths tend to induce undesired fluid motion for manipulation forces such as dielectrophoresis or traveling-wave-dielectrophoresis. Secondly, certain types of physical forces can be generated on molecules, but the 3-D distributions of these physical forces cannot be readily structured for flexible, versatile handling and manipulation of molecules. Thirdly, there is still no general method for manipulating and handling molecules in microfluidic systems and devices.
Microparticles have been used for manipulating molecules in biological fields. One example is the use of magnetic microparticles to harvest and isolate nucleic acid molecules, e.g., mRNAs or DNAs, from a solution suspension. Typically, the separation process takes place in an Eppendorf tube in which paramagnetic particles are mixed with solutions containing target nucleic acid molecules. The modification of the paramagnetic particles' surface molecules allows the binding of the target molecules to paramagnetic particles' surfaces. After incubation of the magnetic particles with nucleic acid molecules in the Eppendorf tube, the nucleic acid molecules are bound to the paramagnetic particles. An external magnetic field is then applied to the Eppendorf tube from one side by using a permanent magnet. All the magnetic particles are collected onto the regions of the tube wall, which are closest to the magnet. Micropipette is then used to pipette out the solutions while the magnetic particles being retained on the tube wall by the magnetic field. This step leaves all the magnetic particles in the tube. New buffer solutions are then introduced into the Eppendorf tube, which is taken away from the magnet. After resuspending magnetic particles into the solution, the new buffer may allow the bound nucleic acid molecules to de-couple from the magnetic particle surfaces. Then a magnet may be applied to attract and trap magnetic particles on the tube wall. Micropipette is then used to pipette solutions out of the tube and to collect the nucleic acid molecules. Recently, similar methods have been used on a chip using paramagnetic beads and an externally applied, off-chip permanent magnet (Fan et al., Anal. Chem., 71(21):4851–9 (1999)). This method has certain limitations. Reducing such permanent magnet size and handling a large number of these small permanent magnets automatically for manipulation of particles in a chip format will be a very difficult, if not impossible, challenge. Thus, the method cannot be readily miniaturized and automated. Furthermore, the permanent magnet-based methods are not applicable to many steps in bioanalytical procedures. Thus, the biochip-system integration based this method will be difficult, if not impossible.
U.S. Pat. No. 5,653,859 discloses a method of analysis or separation comprising: treating a plurality of original, particles to form a subplurality of altered particles from at least some of said plurality of original particles, said subplurality of altered particles having travelling wave field migration properties distinct from those of said plurality of original particles; and producing translatory movement of said subplurality of altered particles and/or said plurality of original particles by travelling wave field migration using conditions such that said translatory movement of said subplurality of altered particle differs from said translatory movement of said plurality of original particles under the same conditions. The physical force used in the methods of U.S. Pat. No. 5,653,859 is limited to the force effected via travelling wave field. In addition, to be used in the methods of U.S. Pat. No. 5,653,859, the original particles have to be partially, but not completely, converted into a subplurality of altered particles because the methods are based upon detecting different translatory movement of the altered particles and the original particles.
In summary, the currently available manipulation methods suffer from the following deficiencies: (1) it is difficult to directly apply effective, physical manipulation forces to many types of molecules because of the relative small dimensions of molecules; and (2) some physical forces that can be generated on molecules often have limitations in 3-D structuring of the force distribution and (3) it is difficult to use currently available biochip-based methods for developing fully automated, miniaturized and integrated biochip systems.
The present invention addresses these and other related needs in the art. It is an objective of the present invention to provide a general method for manipulating a variety of moieties including molecules. It is another objective of the present invention to make full use of a number of force mechanisms effectively for manipulating the moieties. It is still another objective of the present invention to provide for standardized on-chip manipulation procedure, leading to simplification and standardization of the design of microchips and the associated systems. It is yet another objective of the present invention to expand and enhance the capabilities of molecule manipulation with the choice of microparticles with special physical properties. It is yet another objective of the present invention to provide a general, effective procedure for on-chip molecule manipulation that allows for fully integration of biochip-based analytical systems and processes.